The present invention relates generally to cooling systems, and more particularly to a cooling system for cooling an electronic apparatus having an exoergic circuit element (or exoergic element, electronic device, an LSI, or the like). The present invention is suitable, for example, for a cooling system for dissipating heat from various exoergic circuit elements mounted on system boards in a UNIX server or rack-mount server.
Recent developments of electronic apparatuses have required a high-density packing of a server (in particular, a board pitch) or, for example, a low profile server down to about 4 cm in height. On the other hand, the number of exoergic devices, such as a CPU, and the heat dissipation from these circuit elements tends to increase along with high performance and multi-functionality of various circuit elements mounted on a server system board. As the calorification without care would destabilize or deteriorate operations of the circuit elements, and cause thermal damages, various cooling technologies have been proposed for cooling exoergic circuit elements.
A description will now be given of conventional cooling systems with reference to FIGS. 9 to 13.
FIGS. 9 and 10 are schematic block diagrams showing conventional cooling systems 10 and 10A of an air cooling strategy. The cooling system 10 is equipped with a fin heat sink 12 on each of a plurality of exoergic electronic devices (not shown) in a housing 11, and dissipates the heat from the electronic devices (not shown) utilizing heat convection between compulsorily introduced air and a surface of the heat sink 12. The inside air is finally exhausted by the fan 14. On the other hand, the cooling system 10A provides an air duct 16 on the housing 11 in order to enhance the cooling efficiency to the downstream exoergic electronic devices, and provides every heat sink 12 with fresh air through air vents 17 provided in the air duct 16 and an air fan 18. That is, the cooling system 10 supplies downstream electronic devices with air warmed by the upstream heat sink 12, while the cooling system 10A uses the air duct 16 to supply the downstream electronic devices with fresh air. Air fans 14 finally exhaust air from the housing 11 of the cooling systems 10 and 10A.
FIGS. 11 and 12 are schematic block diagrams showing conventional cooling systems of a chilled air cooling strategy. The cooling system 20 arranges the air duct 16 with an evaporator 24. An air chiller (or referred to as a “cooling cycle”) 22 is connected to the evaporator 24 and improves cooling efficiency by introducing chilled air into the electronic apparatus housing 11. That is, the cooling systems 20 and 20A are different in supplying chilled air to the housing 11 from the cooling systems 10 and 10A.
FIG. 13 is a schematic block diagram of a conventional cooling system 30 of a low-temperature liquid cooling type. A compressor 27 circulates coolant in a branch pipe 25, and evaporates the coolant in a cooling module 26 mounted on each heating element, for compulsory cooling. A condenser 28 is provided in the back of the fan 14.
However, the conventional cooling systems cannot satisfactorily meet demands for miniaturization and low profile of the electronic apparatus and cool the electronic apparatus sufficiently.
For example, the cooling systems 10 and 10A introduce the air of operational environment at temperature of 35° C. to 45° C. and has low cooling efficiency. The temperature of the air introduced to the heat sink 12 gradually increases downstream in the air flow direction, and makes it difficult to cool the downstream heating elements. Although the cooling system 10A has the air duct 16, air warmed by the upstream heat sink 12 is similarly supplied to the downstream electronic devices. On the other hand, the mounting interval of the heat sink 12 or the heat sink 12 itself when enlarged in order to improve the cooling performance in the housing 11, would not meet the demands for high-density packaging of the electronic devices and miniaturization and low profile of the housing 11.
The cooling system 20 causes a larger size of the apparatus due to the cooling cycle 22 and air duct 16, and thus is unsuitable for the high-density packaging. Similar to the cooling systems 10 and 10A, the cooling system 20 has low cooling efficiency to the downstream electronic devices. On the other hand, the evaporator 24 has a low heat exchange efficiency when chilling the air. The cooling system 20A is unsuitable for cooling a high power element.
The cooling system 30 provides each heating element with a coolant-use pipe for cooling it, and undesirably making the apparatus large and cooling system complicated. In particular, it is difficult to control a distribution of the coolant among branches in a biphasic state. As the structure of the coolant-use branch pipe 25 becomes complex and the number of connections in the cooling module 26 increases, the reliability and maintenance performance become lower and cost increases.